1. Field of the Invention
The present invention relates to glass fiber reinforced plastic laminate sheets and a method of making the same.
2. Description of the Prior Art
Heretofore continuous processes for producing glass fiber reinforced plastic laminates have employed a run-out table over which a clear cellophane film is drawn. Polymerizable unsaturated polyester resin syrup and randomly oriented glass fibers are applied in a substantially uniform thickness to the cellophane film. A covering cellophane film is applied to form a sandwich which is drawn through a heating zone to accomplish polymerization of the unsaturated polyester resin and produce a rigid, glass fiber reinforced plastic sheet. The sandwich may be flat or may be profiled, e.g., corrugated, prior to curing. The cured laminate will correspondingly be flat or profiled. Customarily, such sheets are transparent or translucent although opaque sheets find utility in building construction, planking, stadium seating. Such sheets are generally referred to as FRP (fiber reinforced plastic) sheets. The unsaturated polyester resin sheets do not weather well for several reasons. The glass fibers have a tendency to bloom at the exposed surface and create multiple wicking sites which allow atmospheric moisture to penetrate beneath the exposed surface of the FRP sheet. Unsaturated polyester resins have a tendency to discolor when exposed to ultraviolet radiation, e.g., atmospheric sunlight. The discoloration of the transparent or translucent FRP sheets diminishes their light transmission properties and renders them less useful when intended for light transmitting installations.
One means for improving the weatherability of FRP sheets has been to apply a film of polyvinyl fluoride (PVF) to the weather-exposed surface of the FRP laminate. The PVF film normally has been applied during the fabrication process as a substitute for a covering cellophane sheet, after the unsaturated polyester resin syrup and glass fibers have been applied to a bottom cellophane sheet. The PVF films have excellent weather resistance and tend to retard the discoloration of the unsaturated polyester resin plastic substances to which they are adhered. However the adhesion of PVF films to unsaturated polyester resin laminates has been unreliable. Alternative procedures for improving the weatherability of FRP panels have been long sought after.